1. Field of the Invention
This invention relates to the methods of preparation of various PbO-based ceramics, particularly ceramics of various forms including thin films and the resulting products of such methods.
2. The Prior Art
In prior art sol-gel precursor solutions, film formation or fiber drawing is only possible when the sol has achieved a certain viscosity as a result of condensation of species within the solution. Hence a relatively narrow window and processing time exists. Additionally, the rheology of the sol changes over the period of drawing. When applied to large-scale commercial production, the film or fibers as drawn initially, differ somewhat in morphology, diameter and other properties from those drawn later, resulting in problems with reproducibility and consistency.
Also the use of unmodified alkoxides in the preparation of precursors suitable for sol-gel processing unfortunately lead to limited shelf life of these precursors since further hydrolysis and condensation of the alkoxy species can alter the nature of the oligomeric species, resulting in a time-dependent effect on the final properties of the product.
Accordingly, there is a need and market for a method for preparing lead-containing ceramics that can be processed to high purity solutions and gels and then to powders, fibers or thin films. The method of the present invention should provide a relatively wide processing window, precursors of prolonged shelf life and otherwise obviate the above prior art shortcomings.
There has now been discovered a method for preparing PbO based ceramics of wide processing window, which process provides durable ceramic products including powders, fibers and thin films of high dielectric constant.
Thus the invention relates to the preparation of various PbO based ceramics of various forms such as powders, fibers and thin films using a wet chemical technique which relies on the use of alkanolamine-modified solutions of lead acetate and various metal alkoxides or salts. Of particular interest is the preparation of ferroelectric films of the PLZT family which have a myriad of electrical and optical applications such as ferroelectric memory, dielectric waveguides, high dielectric constant capacitors, pyroelectric detectors and second harmonic generation. Compositions selected are not restricted to the PLZT systems alone, as the invention is also suitable for preparing lead oxide, lead silicate, lead germanate, lead magnesium niobate materials and other lead oxide containing systems.